Voltage converter

ABSTRACT

A voltage converter comprises an inductive circuit (L) for storing energy during an inductive magnetizing mode and transferring energy during an inductive demagnetizing mode. In addition the voltage converter comprises at least two non-inverting branches ( 12, 13, 14 ) for providing at least two non-inverted output voltages (Va, Vb, Vc) and an inverting branch ( 15 ) for providing an inverted output voltage. The inverting ( 15 ) and non-inverting ( 12, 13, 14 ) branches being parallely coupled to an output ( 10 ) of the inductive circuit (L). The inductive circuit being arranged to transfer energy to the inverting branch ( 15 ) and to one of the at least two non-inverting branches ( 12, 13, 14 ). Through this, the inverted voltage (Vinv) and the corresponding non-inverted output voltage (Va, Vb, Vc) of the one of the at least two non-inverting branches ( 12, 13, 14 ) are having an opposite polarity and a substantially equal magnitude.

This invention relates to a voltage converter, a power management unitand a mobile device comprising such a voltage converter.

The present invention can be used in for example, power supplies ormobile devices such a mobile phones, Personal Digital Assistants (PDA's)or laptops. Voltage converters are generally used to derive multiple DCoutput voltages from a DC input voltage source. These output voltagescan have a higher voltage level than the DC input voltage. Voltageconverters are usually referred to as a DCDC voltage converters orSwitched Mode Power Supplies (SMPS). DCDC converters are generally knownin the art. A voltage converter comprises energy storing means, such asan inductor, to store energy obtained from a DC input voltage source.This energy is subsequently used to generate and sustain the multipleoutput voltages. The energy storing means are cyclically charged andde-charged and the flow of energy from the energy storing means to theoutputs of the voltage converters is regulated by means of programmableswitch devices. It is generally known in the art that also negativevoltages can be provided by using an inverting circuit that is coupledto any of the outputs of the voltage converter.

It is an object of the present invention to provide an improved voltageconverter. To this end the voltage converter comprises:

-   -   an inductive circuit for storing energy during an inductive        magnetizing mode and for transferring energy during an inductive        de-magnetizing mode;    -   at least two non-inverting branches for providing at least two        non-inverted output voltages; and    -   an inverting branch for providing an inverted output voltage;        the inverting and non-inverting branches being parallely coupled        to an output of the inductive circuit, the inductive circuit        being arranged to transfer energy to the inverting branch and to        one of the at least two non-inverting branches, wherein the        inverted voltage and the corresponding non-inverted output        voltage of the one of the at least two non-inverting branches        are having an opposite polarity and a substantially equal        magnitude.

The invention is based on the insight that by coupling the invertingbranch to the output of the inductive circuit rather than to the outputof non-inverting branches considerable savings in required switchdevices can be achieved which allows a far more efficient and morecost-effective design of a voltage converter. The invention is furtherbased upon the insight that the output voltage of both the non-invertingand inverting branches can be determined by the voltage clamp level thatis available at the output of the inductive circuit such that it is nolonger not required to couple the inverting branch to the output of thenon-inverting branches.

In an other embodiment of the voltage converter according to the presentinvention, the inverting branch comprises a capacitive circuit forstoring the transferred energy during the inductive de-magnetizing modeand for releasing the transferred energy during the inductivemagnetizing mode. The capacitor can advantageously act as a battery thatis first charged until a required voltage level is reached and issubsequently de-charged upon request.

In an embodiment of the voltage converter according to the presentinvention, the capacitive circuit is arranged to receive the transferredenergy through an input of the capacitive circuit while an output of thecapacitive circuit is coupled to a ground voltage and wherein thecapacitive circuit is being arranged to release energy through theoutput while the input is coupled to the ground voltage. This embodimenthas the advantage that it provides a convenient way of reversing thepolarity of the voltage across the capacitor.

In an other embodiment of the voltage converter according to the presentinvention, the voltage converter comprises first and second switchdevices for respectively coupling the input (In) and the output (Out) ofthe capacitive circuit to the ground voltage (GND) during respectivelythe inductive magnetizing and de-magnetizing mode. By means of the firstand switch devices, the capacitive circuit can be easily charged andde-charged in a controlled manner.

In an embodiment of the voltage converter according to the presentinvention the voltage converter further comprises a voltage downconversion circuit through which an input voltage is applied to theinductive circuit. Herewith, the amount of charge built-up in theinductive circuit and thus the output voltages of the voltage convertercan be controlled.

In an embodiment of the voltage converter according to the presentinvention, the voltage down-conversion circuit comprises third andfourth switch devices for alternately applying the input voltage and aground voltage to the inductive circuit. This embodiment has theadvantage that the amount of voltage down-conversion can be determinedby the duty-cycle of the third and fourth switch devices. Through this,a programmable voltage down-conversion circuit is obtained.

In an embodiment of the voltage converter according to the presentinvention, at least one of the at least two branches comprises a furtherswitch device for activating the branch. By means of the further switchdevice, the flow of energy from the inductive circuit can be controlled.This means that only if the further switch device is closed, energy willbe transferred to the branch. In addition, if the further switch deviceis closed, the magnitude of the clamp voltage of the inverting branchwill become substantially equal to the magnitude of the clamp voltage ofthe activated non-inverting branch.

In another embodiment of the voltage converter according to the presentinvention, the voltage converter further comprises control means forcontrolling the switch devices. By controlling the switches it ispossible to control the behavior and response of the voltage converter.

These and other aspects of the invention will be elucidated by means ofthe following drawings.

FIG. 1, shows a voltage converter according to the prior art.

FIG. 2, shows the magnetizing current I_(L) through inductor L in aprior art voltage converter.

FIG. 3, shows the voltage drop U_(L) across inductor L in a prior artvoltage converter.

FIG. 4, shows a capacitive DCDC invertor.

FIG. 5, shows a voltage converter comprising a capacitive DCDC inverteraccording to the prior art.

FIG. 6, shows a voltage converter comprising a capacitive DCDC inverteraccording to the present invention.

FIG. 7, shows a switching sequence a voltage converter comprising acapacitive DCDC inverter according to the present invention.

FIG. 8, shows another voltage converter according to an embodiment ofthe invention that comprises input voltage reduction means.

FIG. 1 demonstrates a prior art voltage converter that converts an inputvoltage V_(i) into three clamp voltages V_(a), V_(b) and V_(c). In FIG.1, it is assumed that V_(a)>V_(b)>V_(c). Resistors R_(L1), R_(L2) andR_(L3) represent the loading of the voltage converter. The clampvoltages V_(a), V_(b) and V_(c) are generated according to methodsgenerally known in the art. For example, by controlling the duty-cycleof the inductive magnetizing and de-magnetizing mode in response tomeasuring clamp voltages V_(a), V_(b) and V_(c) or by measuring thecurrents through the circuit loads R_(L1), R_(L2) and R_(L3).

During the inductive magnetizing mode, switch S_(L) is closed(conducting state) whilst D1,S5 and S6 are brought into a non-conductingstate. Apparently, the magnetizing current I_(L) equals I₁. It caneasily be proven by those skilled in the art that I₁ equalsI₁=(V_(i)/L)*t wherein L represents the inductance of the inductor L andt represents time. Therefore, the magnetizing current I_(L) willcontinuously increase with time up to I_(L)equals Imax as is for exampleshown in curve 20 of FIG. 2. It can be easily proven that during theinductive magnetizing mode, current I_(L) transfers an amount of energyE equal to E=½*L*I²max to the inductive circuit L.

During the inductive de-magnetizing mode, switch S_(L) is opened whilstat the same time one of the switching elements D1, S5, S6 is broughtinto a conducting state. This way, the stored energy E=½*L*I²max isdistributed over the output branches 12,13 or 14. By means of example,FIG. 1 assumes that only S5 is brought into a conducting state so thatI_(L)=I₂. It is generally known in the art that inductor L resists tosudden current changes. It can therefore be easily proven that I₂ willstart from Imax and will from thereon linearly decrease, as is shown inFIG. 2 curve 22. The angle α of the ramp 22 of FIG. 2 is determined byL*dI_(L)/dt=(V_(i)−V_(b)+V_(D2)) which means that the angle of the ramp22 is primarily determined by the output voltage V_(b).

V_(b) can be expressed as V_(b)=V_(i)−L*dI_(L)/dt+V_(D2). During theinductive de-magnetizing mode, the voltage across the inductor L ofL*dI_(L)/dt Volt will have a negative polarity, as is for example shownin FIG. 3 curve 32. It will however be apparent that −L*dI_(L)/dt willhave a positive contribution to the output voltage V_(b)·V_(D2)represents the voltage drop across the diode D2 which typically liestypically between 0.3 and 0.7 Volts depending on the technology used.Diodes D1,D2 and D3 are applied to prevent current leakage from theoutputs of the voltage converter towards the internal node 10. DiodesD1, D2 and D3 can be omitted in case switches S5, S6 are strictlyuni-directional i.e. they conduct only from internal node 10 to theoutputs. This is for example the case when the switches S5, S6 areconstructed by means of a pair of P-mos transistors that areanti-serially coupled. It will be apparent that in this case branch 12must also comprise a switch device. If switches S5 and S6 are opened,current I₂ will start flowing though branch 12. If switch S5 closed andS6 is left open, a voltage of V_(b)−VD2 will be imposed on internal node10. Since this is a lower voltage than V_(a), diode D1 will be turnedoff and I₂ will start flowing through the second branch 13. Likewise,closing S6 will impose a voltage of V_(c)−V_(D3) on internal node 10which will turn diodes D1 and D2 off. By operating switches S_(L),S5 andS6 in a controlled manner it is thus possible to magnetize andde-magnetize the inductor L and to transfer the energy from inductor Lto each one of the branches 12,13 and 14. Capacitor C1 acts as an DCinput buffer that protects the input line against the high frequencyswitching input currents and the switching noise of the voltageconverter. Capacitors C2, C3 and C4 serve as DC output buffers. Theirfunction is firstly to smoothen the high frequency output currents andsecondly, to assure a continuous output voltage during periods of timewhen no charge is provided to the branches of the voltage converter. Asa consequence of this, the voltages across C2,C3 and C4 will show aslight AC ripple. However, this is of little consequence sincecapacitors C2,C3 and C4 are recharged fast enough by the inductivecircuit.

FIG. 2 shows the magnetizing current I_(L) flowing through inductor L.The rising edges 20 represent the charging or magnetizing of theinductor (S_(L) is closed). During the inductive maximizing mode themagnetizing current I_(L) increases until S_(L) is opened. It can easilybe proven that I_(L) equals V_(i)*t/L wherein t represents time and L isthe inductance of the inductor L. Once S_(L) is opened, current I_(L)equals Imax and will exhibit a falling edge 22 as is shown in FIG. 2. Itcan be easily proven that this falling edge can be expressed asdI_(L)/dt=(V_(i)−Vout+V_(D))/L wherein V_(i) represents the inputvoltage. Vout represents any of the output voltages V_(a), V_(b),V_(c)of FIG. 1, V_(D) represents the voltage drop across diodes D1,D2 and D3.when the diodes are in a conducting state.

FIG. 3 shows the voltage drop U_(L) across inductor L which can beexpressed as U_(L)=L*dI_(L)/dt. This results in a positive polarity 30of the voltage U_(L) during the rising edges 20 of I_(L) and a negativepolarity 32 of the voltage U_(L) during the falling edges 22 of I_(L).

FIG. 4 shows a DCDC capacitive voltage inverter. Shown is a capacitorCpump that is charged through an input voltage source V_(i). During thecharging, switches S4 and S2 are closed whilst switches S_(L) and S7 areopened. Through this, Cpump will be charged until the voltage dropacross Cpump corresponds to V_(i) and is having a polarity as shown inFIG. 4. Once Cpump is fully charged, switches S4 and S2 are finallyopened and switches S_(L) and S7 are closed. Because of this, Cpump iscoupled to the output capacitive voltage inverter to deliver an outputvoltage Vinv that is having the same magnitude as V_(i) but is having anopposite polarity. Capacitor Co is a DC output buffer that smoothens thehigh frequency output current of the converter and to provide the outputvoltage Vinv to the load of the capacitive DCDC inverter when the pumpcapacitor Cpump is recharged.

FIG. 5, shows the combination of the prior art DCDC voltage converter asshown in FIG. 1 and the capacitive DCDC voltage inverter as discussed inFIG. 4. Capacitor Cpump is coupled to the outputs of branches 12, 13 and14 by means of switches S4, S′4 and S″4 that are operated in analternate fashion. By closing e.g. switches S4 and S2, pump capacitorCpump is charged with voltage V_(c). By closing S7 and S1 and openingS4, S′4, S″4 and S2 the output voltage Vinv becomes equal to −V_(c).

FIG. 6, shows a DCDC voltage converter according to the presentinvention. Shown is a capacitive DCDC inverter that is coupled to theinternal node 10. Through this Cpump is charged with the voltageavailable at node 10 during the inductive de-magnetizing mode. Aspreviously discussed, this voltage is determined by the input voltage Viand the voltage drop across inductor L. Apparently, the voltage dropacross the inductor is determined by the currents I2 and I′2 that aredrawn from it during the de-magnetizing mode. It will be apparent tothose skilled in the art that through this, the output voltage Vinv canhave a substantially equal magnitude than any one of the clamp voltagesV_(a), V_(b) or V_(c) depending on which of the non-inverting branches12,13 or 14 is activated. By providing control means (82), the dutycycle of the switches S1, S2, S5, S6, S7 can be controlled in order toinfluence the behavior of the voltage converter. This embodimentprovides the advantage that only a limited amount of extra switches arerequired i.e. S6 and S7 which makes the circuit much easier to integrateat lower costs and less requirements for the control of the switches.

FIG. 7 shows, by means of example, switching cycles for controlling theswitches S1, S6 and S7 of FIG. 6. It is assumed that energy is providedto the non-inverting branch 14 (deliver on demand) and to thenon-inverting branch. This means that switches S5 and S2 are closed andS6 and S7 are left open. It will be apparent to those skilled in the artthat the voltage level at node 10, will substantially correspond to theclamp voltage V_(b). This means, that the voltage across Cpump willbecome V_(b) as well. During the next inductive magnetizing mode 72,switches S1 and S7 are closed such that current I₁ will start flowingfor charging inductor L with energy whilst the output voltage of theinverting branch Vinv will become −V_(b). Once Cpump is coupled to theoutput of the inverting branch it will be apparent that the voltageacross the capacitor Cpump will somewhat decrease. Therefore, during thenext inductive de-magnetizing mode, S1 and S7 are re-opened and S6 isclosed. This allows Cpump to be replenished with energy such that againa voltage drop of V_(b) Volts will be across the capacitor Cpump.

FIG. 8, shows a DCDC voltage converter wherein by means of switches S3and S4, alternately a ground voltage GND and an input voltage V_(i) arecoupled to the inductor L. for reducing the average value of the inputvoltage V_(i). It will be apparent to those skilled in the art that areduction of the input value can advantageously be used to influence theoutput voltages of the DCDC voltage converter.

It is to be noted that the above-mentioned embodiments illustrate ratherthan limit the invention, and that those skilled in the art will be ableto design many alternative embodiments without departing from the scopeof the appended claims. The word “comprising” does not exclude thepresence of elements or steps other than those listed in a claim. Theword “a” or “an” preceding an element does not exclude the presence of aplurality of such elements. The mere fact that certain measures arerecited in mutually different dependent claims does not indicate that acombination of these measures cannot be used to advantage.

1. A voltage converter comprising: an inductive circuit for storingenergy during an inductive magnetizing mode and transferring energyduring an inductive de-magnetizing mode; at least two non-invertingbranches for providing at least two non-inverted output voltages and aninverting branch for providing an inverted output voltage; the invertingand non-inverting branches being parallely coupled to an output of theinductive circuit the inductive circuit being arranged to transferenergy to the inverting branch and to one of the at least twonon-inverting branches that is activated, wherein the inverted voltageand the corresponding non-inverted output voltage of the one of the atleast two non-inverting branches have an opposite polarity and asubstantially equal magnitude; and wherein said magnitude is determinedby the selection of the one non-inverting branch that is activated. 2.The voltage converter according to claim 1, wherein the inverting branchcomprises a capacitive circuit for storing the energy that istransferred during the inductive de-magnetizing mode and for releasingthe transferred energy during the inductive magnetizing mode.
 3. Thevoltage converter according to claim 2, wherein the capacitive circuitis arranged to receive the transferred energy through an input of thecapacitive circuit while an output of the capacitive circuit is coupledto a ground voltage and wherein the capacitive circuit is further beingarranged to release energy through the output while the input is coupledto the ground voltage.
 4. The voltage converter according to claim 3,comprising first and second switch devices for respectively coupling theinput and the output of the capacitive circuit to the ground voltageduring respectively the inductive magnetizing and de-magnetizing mode.5. The voltage converter according to claim 1, wherein the voltageconverter further comprises a voltage down conversion circuit throughwhich an input voltage is applied to the inductive circuit.
 6. Thevoltage converter according to claim 5, wherein the voltagedown-conversion circuit comprises third and fourth switch devices foralternately applying the input voltage and a ground voltage to theinductive circuit.
 7. The voltage converter according to claim 1,wherein at least one of the at least two branches comprises a furtherswitch device for activating the branch.
 8. The voltage converteraccording to claim 1, wherein the voltage converter further comprisescontrol means for controlling the switch devices.
 9. A power managementunit comprising a voltage converter according to claim
 1. 10. A mobiledevice comprising a power management unit according to claim 9.